• 目錄
  1、模型在軟件開發(fā)中的作用
  2、誕生背景
  3、整體架構(gòu)
  4、核心流程

模型在軟件開發(fā)中的作用

后臺下發(fā)的數(shù)據(jù)格式一般是JSON格式，我們可以方便的將其轉(zhuǎn)換為字典，即便如此，在使用時候仍然存在一些問題，如key值直接寫在代碼中，不能一眼看清下發(fā)的數(shù)據(jù)結(jié)構(gòu)，維護(hù)起來極其不方便，而且通過字典數(shù)組的方式獲取數(shù)據(jù)一個不小心就會crash，最主要的是會花費(fèi)很多時間在字段匹配上，這時候模型的作用就體現(xiàn)出來了

@interface Person : NSObject
// 接口文檔的鏈接注釋在這里
@property (nonatomic, copy) NSString *name;      // 名字
@property (nonatomic, assign) NSUInterger age;   // 年齡
...

@end

如上，接口下發(fā)的數(shù)據(jù)結(jié)構(gòu)一目了然，直接訪問屬性方便、安全，而且可以直接定位到相關(guān)文檔，也便于后續(xù)拓展，這就是抽象的力量

誕生背景

將后臺下發(fā)的數(shù)據(jù)結(jié)構(gòu)抽象成Model，給程序員帶來極大的方便，但是隨著業(yè)務(wù)的爆發(fā)，這種數(shù)據(jù)轉(zhuǎn)模型的代碼會急劇增加，而且各個業(yè)務(wù)接口的數(shù)據(jù)結(jié)構(gòu)幾乎都不相同，轉(zhuǎn)換的代價會越來越大，并且難于維護(hù)，每次修改數(shù)據(jù)結(jié)構(gòu)都要修改數(shù)據(jù)轉(zhuǎn)模型部分的代碼，這大大降低了敏捷分開的迭代的速度，這時候程序員迫切需要一種數(shù)據(jù)自動轉(zhuǎn)模型的工具，于是YYModel誕生了

整體架構(gòu)

一共有兩個實現(xiàn)文件NSObject+YYModel和YYClassInfo：3個分類，6個類，如下

YYClassInfo是類對象的OC封裝，內(nèi)部聚合了Ivar ivar、Method method、objc_property_t property
如下：

/**
 Class information for a class.
 */
@interface YYClassInfo : NSObject
@property (nonatomic, assign, readonly) Class cls; ///< class object
@property (nullable, nonatomic, assign, readonly) Class superCls; ///< super class object
@property (nullable, nonatomic, assign, readonly) Class metaCls;  ///< class's meta class object
@property (nonatomic, readonly) BOOL isMeta; ///< whether this class is meta class
@property (nonatomic, strong, readonly) NSString *name; ///< class name
@property (nullable, nonatomic, strong, readonly) YYClassInfo *superClassInfo; ///< super class's class info
@property (nullable, nonatomic, strong, readonly) NSDictionary<NSString *, YYClassIvarInfo *> *ivarInfos; ///< ivars
@property (nullable, nonatomic, strong, readonly) NSDictionary<NSString *, YYClassMethodInfo *> *methodInfos; ///< methods
@property (nullable, nonatomic, strong, readonly) NSDictionary<NSString *, YYClassPropertyInfo *> *propertyInfos; ///< properties

公有方法有四個如下：類信息更新狀態(tài)存取方法，和兩個初始化器

- (void)setNeedUpdate;
- (BOOL)needUpdate;
+ (nullable instancetype)classInfoWithClass:(Class)cls;
+ (nullable instancetype)classInfoWithClassName:(NSString *)className;

NSObject+YYModel中定義了兩個內(nèi)部類_YYModelPropertyMeta、_YYModelMeta,分別表示模型中的屬性和類信息，YYClassPropertyInfo 和YYClassInfo可以理解為單純的數(shù)據(jù)結(jié)構(gòu)，而_YYModelPropertyMeta、_YYModelMeta則是組合在一起的模型單元，分別扮演樹枝節(jié)點(diǎn)和葉子節(jié)點(diǎn)角色

/// A property info in object model.
@interface _YYModelPropertyMeta : NSObject {
    @package
    NSString *_name;             ///< property's name
    YYEncodingType _type;        ///< property's type
    YYEncodingNSType _nsType;    ///< property's Foundation type
    BOOL _isCNumber;             ///< is c number type
    Class _cls;                  ///< property's class, or nil
    Class _genericCls;           ///< container's generic class, or nil if threr's no generic class
    SEL _getter;                 ///< getter, or nil if the instances cannot respond
    SEL _setter;                 ///< setter, or nil if the instances cannot respond
    BOOL _isKVCCompatible;       ///< YES if it can access with key-value coding
    BOOL _isStructAvailableForKeyedArchiver; ///< YES if the struct can encoded with keyed archiver/unarchiver
    BOOL _hasCustomClassFromDictionary; ///< class/generic class implements +modelCustomClassForDictionary:
    
    /*
     property->key:       _mappedToKey:key     _mappedToKeyPath:nil            _mappedToKeyArray:nil
     property->keyPath:   _mappedToKey:keyPath _mappedToKeyPath:keyPath(array) _mappedToKeyArray:nil
     property->keys:      _mappedToKey:keys[0] _mappedToKeyPath:nil/keyPath    _mappedToKeyArray:keys(array)
     */
    NSString *_mappedToKey;      ///< the key mapped to
    NSArray *_mappedToKeyPath;   ///< the key path mapped to (nil if the name is not key path)
    NSArray *_mappedToKeyArray;  ///< the key(NSString) or keyPath(NSArray) array (nil if not mapped to multiple keys)
    YYClassPropertyInfo *_info;  ///< property's info
    _YYModelPropertyMeta *_next; ///< next meta if there are multiple properties mapped to the same key.
}
@end

/// A class info in object model.
@interface _YYModelMeta : NSObject {
    @package
    YYClassInfo *_classInfo;
    /// Key:mapped key and key path, Value:_YYModelPropertyMeta.
    NSDictionary *_mapper;
    /// Array<_YYModelPropertyMeta>, all property meta of this model.
    NSArray *_allPropertyMetas;
    /// Array<_YYModelPropertyMeta>, property meta which is mapped to a key path.
    NSArray *_keyPathPropertyMetas;
    /// Array<_YYModelPropertyMeta>, property meta which is mapped to multi keys.
    NSArray *_multiKeysPropertyMetas;
    /// The number of mapped key (and key path), same to _mapper.count.
    NSUInteger _keyMappedCount;
    /// Model class type.
    YYEncodingNSType _nsType;
    
    BOOL _hasCustomWillTransformFromDictionary;
    BOOL _hasCustomTransformFromDictionary;
    BOOL _hasCustomTransformToDictionary;
    BOOL _hasCustomClassFromDictionary;
}
@end

頭文件定義了一系列的公有方法，包含初始化器和工具函數(shù)，這里不再詳述

核心流程

先調(diào)用_yy_dictionaryWithJSON把json轉(zhuǎn)成字典，然后調(diào)用modelWithDictionary生成model

+ (instancetype)modelWithJSON:(id)json {
    NSDictionary *dic = [self _yy_dictionaryWithJSON:json];
    return [self modelWithDictionary:dic];
}

下面這個函數(shù)用來構(gòu)造類信息和參數(shù)校驗

+ (instancetype)modelWithDictionary:(NSDictionary *)dictionary {
    if (!dictionary || dictionary == (id)kCFNull) return nil;
    if (![dictionary isKindOfClass:[NSDictionary class]]) return nil;
    
    Class cls = [self class];
    _YYModelMeta *modelMeta = [_YYModelMeta metaWithClass:cls];
    if (modelMeta->_hasCustomClassFromDictionary) {
        cls = [cls modelCustomClassForDictionary:dictionary] ?: cls;
    }
    
    NSObject *one = [cls new];
    if ([one modelSetWithDictionary:dictionary]) return one;
    return nil;
}

初始化模型上下文，遍歷所有屬性，進(jìn)行賦值

- (BOOL)modelSetWithDictionary:(NSDictionary *)dic {
    if (!dic || dic == (id)kCFNull) return NO;
    if (![dic isKindOfClass:[NSDictionary class]]) return NO;
    
    // 構(gòu)造_YYModelMeta 模型
    _YYModelMeta *modelMeta = [_YYModelMeta metaWithClass:object_getClass(self)];
    if (modelMeta->_keyMappedCount == 0) return NO;
    
    if (modelMeta->_hasCustomWillTransformFromDictionary) {
        dic = [((id<YYModel>)self) modelCustomWillTransformFromDictionary:dic];
        if (![dic isKindOfClass:[NSDictionary class]]) return NO;
    }
    
    ModelSetContext context = {0};
    context.modelMeta = (__bridge void *)(modelMeta);
    context.model = (__bridge void *)(self);
    context.dictionary = (__bridge void *)(dic);
    
    if (modelMeta->_keyMappedCount >= CFDictionaryGetCount((CFDictionaryRef)dic)) {
        // 字典中的每個鍵值對調(diào)用 ModelSetWithDictionaryFunction
        // ModelSetWithDictionaryFunction 通過字典設(shè)置模型
        CFDictionaryApplyFunction((CFDictionaryRef)dic, ModelSetWithDictionaryFunction, &context);
        if (modelMeta->_keyPathPropertyMetas) {
            // 每個映射 keyPath 的屬性元執(zhí)行 ModelSetWithPropertyMetaArrayFunction
            CFArrayApplyFunction((CFArrayRef)modelMeta->_keyPathPropertyMetas,
                                 CFRangeMake(0, CFArrayGetCount((CFArrayRef)modelMeta->_keyPathPropertyMetas)),
                                 ModelSetWithPropertyMetaArrayFunction,
                                 &context);
        }
        if (modelMeta->_multiKeysPropertyMetas) {
            // 每個映射多個 key 的屬性元執(zhí)行 ModelSetWithPropertyMetaArrayFunction
            CFArrayApplyFunction((CFArrayRef)modelMeta->_multiKeysPropertyMetas,
                                 CFRangeMake(0, CFArrayGetCount((CFArrayRef)modelMeta->_multiKeysPropertyMetas)),
                                 ModelSetWithPropertyMetaArrayFunction,
                                 &context);
        }
    } else { 
        // 每個 modelMeta 屬性元執(zhí)行 ModelSetWithPropertyMetaArrayFunction
        CFArrayApplyFunction((CFArrayRef)modelMeta->_allPropertyMetas,
                             CFRangeMake(0, modelMeta->_keyMappedCount),
                             ModelSetWithPropertyMetaArrayFunction,
                             &context);
    }
    
    if (modelMeta->_hasCustomTransformFromDictionary) {
        return [((id<YYModel>)self) modelCustomTransformFromDictionary:dic];
    }
    
    return YES;
}

最終調(diào)用到ModelSetValueForProperty函數(shù)，實現(xiàn)單個屬性的賦值，通過objc_msgSend函數(shù)直接調(diào)用屬性的setter方法進(jìn)行賦值